320 research outputs found
Kinetic equation for strongly interacting dense Fermi systems
We review the non-relativistic Green's-function approach to the kinetic
equations for Fermi liquids far from equilibrium. The emphasis is on the
consistent treatment of the off-shell motion between collisions and on the
non-instant and non-local picture of binary collisions. The resulting kinetic
equation is of the Boltzmann type, and it represents an interpolation between
the theory of transport in metals and the theory of moderately dense gases. The
free motion of particles is renormalised by various mean field and mass
corrections in the spirit of Landau's quasiparticles in metals. The collisions
are non-local in the spirit of Enskog's theory of non-ideal gases. The
collisions are moreover non-instant, a feature which is absent in the theory of
gases, but which is shown to be important for dense Fermi systems. In spite of
its formal complexity, the presented theory has a simple implementation within
the Monte-Carlo simulation schemes. Applications in nuclear physics are given
for heavy-ion reactions and the results are compared with the former theory and
recent experimental data. The effect of the off-shell motion and the non-local
and non-instant collisions on the dynamics of the system can be characterised
in terms of thermodynamic functions such as the energy density or the pressure
tensor. Non-equilibrium counterparts of these functions and the corresponding
balance equations are derived and discussed from two points of view. Firstly,
they are used to prove the conservation laws. Secondly, the role of individual
microscopic mechanisms in fluxes of particles and momenta and in
transformations of the energy is clarified.Comment: Boo
Nonlocal Kinetic Equation and Simulations of Heavy Ion Reactions
A kinetic equation which combines the quasiparticle drift of Landau's
equation with a dissipation governed by a nonlocal and noninstantaneous
scattering integral in the spirit of Enskog corrections is discussed. Numerical
values of the off-shell contribution to the Wigner distribution, of the
collision duration and of the collision nonlocality are presented for different
realistic potentials. On preliminary results we show that simulations of
quantum molecular dynamics extended by the nonlocal treatment of collisions
leads to a broader proton distribution bringing the theoretical spectra closer
towards the experimental values than the local approach.Comment: Proceedings of the Erice School, published as Vol. 42 of "Progress in
Particle and Nuclear Physics" by ELSEVIE
Nonlinear relaxation field in charged systems under high electric fields
The influence of an external electric field on the current in charged systems
is investigated. The results from the classical hierarchy of density matrices
are compared with the results from the quantum kinetic theory. The kinetic
theory yields a systematic treatment of the nonlinear current beyond linear
response. To this end the dynamically screened and field-dependent
Lenard-Balescu equation is integrated analytically and the nonlinear relaxation
field is calculated. The classical linear response result known as Debye -
Onsager relaxation effect is only obtained if asymmetric screening is assumed.
Considering the kinetic equation of one specie the other species have to be
screened dynamically while the screening with the same specie itself has to be
performed statically. Different other approximations are discussed and
compared.Comment: language correction
Short time dynamics with initial correlations
The short-time dynamics of correlated systems is strongly influenced by
initial correlations giving rise to an additional collision integral in the
non-Markovian kinetic equation. Exact cancellation of the two integrals is
found if the initial state is thermal equilibrium which is an important
consistency criterion. Analytical results are given for the time evolution of
the correlation energy which are confirmed by comparisons with molecular
dynamics simulations (MD)
Electronic transport properties through thiophenes on switchable domains
The electronic transport of electrons and holes through stacks of
,\ome ga-dicyano-,'-dibutyl- quaterthiophene (DCNDBQT)
as part of a nov el organic ferroic field-effect transistor (OFFET) is
investigated. The novel ap plication of a ferroelectric instead of a dielectric
substrate provides the poss ibility to switch bit-wise the ferroelectric
domains and to employ the polarizat ion of these domains as a gate field in an
organic semiconductor. A device conta ining very thin DCNDBQT films of around
20 nm thickness is intended to be suitab le for logical as well as optical
applications. We investigate the device proper ties with the help of a
phenomenological model called multilayer organic light-e mitting diodes
(MOLED), which was extended to transverse fields. The results sho wed, that
space charge and image charge effects play a crucial role in these org anic
devices
Enhancement of pairing due to the presence of resonant cavities
A correlated fermion system is considered surrounding a finite cavity with
virtual levels. The pairing properties are calculated and the influence of the
cavity is demonstrated. To this end the Gell-Mann and Goldberger formula is
generalized to many-body systems. We find a possible enhancement of pairing
temperature if the Fermi momentum times the cavity radius fulfills a certain
resonance condition which suggests an experimental realization.Comment: 4 pages 2 figure
In-medium two-nucleon properties in high electric fields
The quantum mechanical two - particle problem is considered in hot dense
nuclear matter under the influence of a strong electric field such as the field
of the residual nucleus in heavy - ion reactions. A generalized
Galitskii-Bethe-Salpeter equation is derived and solved which includes
retardation and field effects. Compared with the in-medium properties in the
zero-field case, bound states are turned into resonances and the scattering
phase shifts are modified. Four effects are observed due to the applied field:
(i) A suppression of the Pauli-blocking below nuclear matter densities, (ii)
the onset of pairing occurs already at higher temperatures due to the field,
(iii) a field dependent finite lifetime of deuterons and (iv) the imaginary
part of the quasiparticle self-energy changes its sign for special values of
density and temperatures indicating a phase instability. The latter effect may
influence the fragmentation processes. The lifetime of deuterons in a strong
Coulomb field is given explicitly.Comment: ps file + 7 figures (eps
Anomalous radial expansion in central heavy-ion reactions
The expansion velocity profile in central heavy-ion reactions in the Fermi
energy domain is examined. The radial expansion is non-hubblean and in the
surface region it scales proportional to a higher exponent () of
the radius. The anomalous expansion velocity profile is accompanied by a power
law nucleon density profile in the surface region. Both these features of
central heavy-ion reactions disappear at higher energies, and the system
follows a uniform Hubble expansion ()
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